Rotatable idler for undercarriage system in a track-type machine

ABSTRACT

An undercarriage system for a track-type machine includes a ground engaging track, and an idler for the ground engaging track having a hub formed of a relatively lower hardness metallic material, and a compound annular rim capping the hub and being formed of a relatively higher hardness metallic material. The hub includes a radially projecting outer spine, which is annular and concentric with an idler mounting bore defined by an inner peripheral surface of the hub. First and second rim components of the compound annular rim abut one another and sandwich the radially projecting outer spine. Each of the first and second abutting rim components includes a stepped profile. The idler may include a remanufactured idler having a reusable hub and replacement compound annular rim.

TECHNICAL FIELD

The present disclosure relates generally to undercarriage systems in track-type machines, and relates more particularly to capping a one-piece hub formed of a relatively lower hardness metallic material with a compound annular rim formed of a relatively higher hardness metallic material.

BACKGROUND

Track-type machines are used in a wide variety of rugged service environments. The use of ground engaging tracks rather than wheels can provide enhanced traction, stability, and robustness to a machine system over what might otherwise be available. Mining, construction, landfills, forestry, and still other service environments are notable examples of where track-type machines are advantageously used. A typical undercarriage system in a track-type machine includes a plurality of track shoes coupled together in an endless track chain by way of a set of track links, and extending about a drive sprocket and one or more rotatable idlers. Many undercarriage system components experience metal-on-metal wear during service. In addition, abrasive materials are present at most worksites where track-type machines are used. The metal-on-metal contact between and among undercarriage system components, exacerbated by abrasive materials, can subject undercarriage systems to substantial wear.

Rotation of the one or more drive sprockets and idler against components of the track such as the track links and/or track shoes, and particularly where abrasive materials intrude between the drive sprocket or idler and the track, can wear away material such that dimensions, contact patterns, and other geometric properties of the subject components tend to change over time. Many undercarriage systems include mechanisms adapted to compensate for wear and the resulting geometric changes. Various types of idler recoil systems are used in track-type machines at least in part to maintain a tensioned state of the track, while allowing chunks of debris such as rocks and the like to occasionally pass between the rotating idler and the track links or track shoes. Such idler recoil systems may inherently, or by way of manual adjustments, compensate for the wear induced geometric changes mentioned above. For instance, over time an outer surface of a rotatable idler can lose material such that a diameter of the idler is reduced. Where equipped with an idler recoil system, an actuator or other compensating mechanism can “push” the idler against the track such that a suitable tensioned state of the track is maintained despite a reduction in idler diameter or other wear induced geometric changes.

Although the use of idler recoil systems and the like can extend track service life over what might otherwise be possible, eventually wear on the idler and/or other undercarriage system components necessitates track servicing or rebuild if efficient use of the machine, and in some cases any use, is to continue. For reasons which will be readily apparent, it is desirable upon rebuild or servicing to reuse at least some of the undercarriage system components rather than purchasing all new parts. To this end, rotatable idlers which have been subjected to field service wear may sometimes be repaired and/or remanufactured. One technique for returning a worn idler to a condition suitable for returning to service involves adding material to an outer surface of the worn idler to return the idler to a size and/or shape similar to that of a new idler. Repair technicians may perform a very labor intensive process known in the art as “hard facing” in which numerous layers of material are deposited one upon the other on the outer surface of the idler. While in many instances a hard facing process can be economically superior over purchasing a new idler, idlers repaired in this manner may have reduced robustness and greater susceptibility to certain types of wear than a new idler, and suffer from other shortcomings.

SUMMARY OF THE DISCLOSURE

In one aspect, a rotatable idler for an undercarriage system in a track-type machine includes a one-piece hub defining an axis of rotation and being formed of a relatively lower hardness metallic material. The one-piece hub includes an outer peripheral surface, a first and a second end surface located on first and second axial sides of the one-piece hub, an inner peripheral surface defining an idler mounting bore, and a radially projecting outer spine. The radially projecting outer spine includes an annular configuration circumferential of the axis of rotation, and is positioned axially between the first and second end surfaces. The rotatable idler further includes a compound annular rim coaxial with the one-piece hub and being formed of a relatively higher hardness metallic material, the compound annular rim capping the one-piece hub and including an inner rim surface, and a track contacting outer rim surface having a crowned profile. The compound annular rim further includes a first and a second rim component each having a stepped profile. Each of the rim components further includes an outboard shoulder segment relatively tightly fitted upon the outer peripheral surface and located axially outward of the radially projecting outer spine, and an inboard crown segment relatively loosely fitted upon the outer peripheral surface and axially overlapping the radially projecting outer spine.

In another aspect, a method of making a rotatable idler for an undercarriage system in a track-type machine includes capping a one-piece hub formed of a relatively lower hardness metallic material and defining an axis of rotation with a compound annular rim formed of a relatively higher hardness metallic material. The method further includes sandwiching a radially projecting outer spine of the one piece hub axially between abutting rim components of the compound annular rim during capping the one-piece hub, and attaching the compound annular rim to the one-piece hub.

In still another aspect, an undercarriage system for a track-type machine includes a ground engaging track having a plurality of track shoes, and a plurality of track links coupling together the track shoes in an endless track chain. The undercarriage system further includes an idler for the ground engaging track including an idler body having a hub formed of a relatively lower hardness metallic material, and a compound annular rim capping the hub and being formed of a relatively higher hardness metallic material. The hub includes an inner peripheral surface defining an idler mounting bore, an outer peripheral surface, and a radially projecting outer spine. The radially projecting outer spine includes an annular configuration and is concentric with the idler mounting bore. The compound annular rim includes an inner rim surface, a track contacting outer rim surface having a crowned profile, and first and second abutting rim components sandwiching the radially projecting outer spine, each of the first and second abutting rim components having a stepped profile and including a portion of the inner rim surface and a portion of the track contacting outer rim surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of a machine according to one embodiment;

FIG. 2 is a perspective view of an idler for an undercarriage system in a track-type machine, according to one embodiment;

FIG. 3 is a sectioned view through a portion of an undercarriage system having an idler, according to one embodiment;

FIG. 4 is a sectioned view through an idler, according to another embodiment; and

FIG. 5 is a sectioned view through an idler according to yet another embodiment.

DETAILED DESCRIPTION

Referring to FIG. 1, there is shown a machine 10 according to one embodiment. Machine 10 includes a frame 12, and an undercarriage system 14 coupled with frame 12. An operator cab 13 is positioned upon frame 12, and an implement 15 is also coupled with frame 12. Machine 10 is shown in the context of a track-type tractor, however, it should be appreciated that machine 10 might include an excavator, a track loader, or still another type of machine. Implement 15 is shown as a blade, however, it will similarly be appreciated that a variety of different implements such as a bucket or the like might alternatively be used.

Undercarriage system 14 includes a drive sprocket 22, a rotatable idler 30, a track roller frame 28, and a ground engaging track 16. Track 16 may include one of two tracks positioned at opposite sides of machine 10 in a conventional manner. Accordingly, the present description of track 16 and associated components of undercarriage system 14 should be understood to refer similarly to a second track positioned at an opposite side of machine 10. Track 16 may include a track chain 17 having a plurality of track shoes 18 coupled together in track chain 17 and extending in an endless loop about drive sprocket 22 and idler 30. One or more carrier rollers 24 may be coupled with track roller frame 28 in a conventional manner, as may a plurality of lower rollers 26. Undercarriage system 14 is shown in the context of an oval track design, however, it should be appreciated that a high-drive track system or the like might be used without departing from the scope of the present disclosure.

Referring also to FIG. 2, rotatable idler 30 may include a one-piece hub 32 defining an axis of rotation Z. Hub 32 may include an outer peripheral surface 34, an inner peripheral surface 44 defining an idler mounting bore 33, and a compound annular rim 50 coaxial with and capping one-piece hub 32. As used herein, the term “capping” should be understood to mean that rim 50 provides an outermost covering of idler 30 and overlies substantially all of outer peripheral surface 34. Thus, components positioned between an outer peripheral surface of an idler hub and a track contacting surface of the associated idler would not in and of themselves be understood as “capping” the idler hub. Rim 50 may include an inner rim surface 52, and a track contacting outer rim surface 54 having a crowned profile. A first axial side 40 of hub 32 is shown in FIG. 2, and a second axial side 42 may be substantially a mirror image of first axial side 40. Rim 50 may further include a first rim component 56 a and a second rim component 56 b, each of which may include approximately one-half of each of outer rim surface 54 and inner rim surface 52. Each of rim components 56 a and 56 b may include a stepped profile, in other words a stepped profile in an axial direction, the significance of which will be further apparent from the following description. As also further discussed herein, idler 30 and other contemplated embodiments may be uniquely configured for high durability and wear resistance based at least in part upon selection of suitable materials for hub 32 and rim 50, as well as the use of coupling strategies between rim 50 and hub 32, and geometry of the respective components.

Turning now to FIG. 3, there is shown a sectioned view through a portion of undercarriage system 14 and in a section plane which includes a plane of axis of rotation Z. The configuration of idler 30 shown in FIG. 3 may be similar or identical at any other section plane which includes all of axis Z. Outer rim surface 54 of compound annular rim 50 is shown in contact with track pins 21 which couple together two sets of track links 20, which are in turn coupled with track shoes 18. Also shown in FIG. 3 is a first axial end surface 36 of hub 32 located on first axial side 40, and a second axial end surface 38 of hub 32 located on second axial side 42. It may be noted that each of axial side surfaces 36 and 38 includes a bathtub shaped profile of rotation about axis Z. Still further illustrated in FIG. 3 is a radially projecting outer spine 48 of hub 32. Outer spine 48 may include an annular configuration circumferential of axis Z, and may further be a continuous outer spine having a uniform cross sectional profile about axis Z, similar to what is shown in FIG. 3. Outer spine 48 may be positioned axially between first end surface 36 and second end surface 38, and may be concentric with bore 44. Rim components 56 a and 56 b may likewise be concentric with bore 44 and thus coaxial with hub 32.

Also shown in FIG. 3 are additional features of compound annular rim 50. As noted above, compound annular rim 50 may be coaxial with hub 32. Compound annular rim 50 may be understood as “compound” due at least in part to the fact that it is formed from multiple subcomponents such as first rim component 56 a and second rim component 56 b. As alluded to above, selection of certain materials for idler 30 is contemplated to provide enhanced durability and wear resistance. To this end, each of rim components 56 a and 56 b may be formed from a relatively higher hardness metallic material. Hub 32 may be formed of a relatively lower hardness metallic material. In one embodiment, hub 32 may include a casting formed from mild steel, and each of rim components 56 a and 56 b may include a machined casting or otherwise formed relatively harder steel. Example materials for rim components 56 a and 56 b include alloys such as 4340 steel, AISI 420 steel, AISI 440 steel, or Hadfield steel. The selection of suitable materials may be based at least in part upon intended service conditions, as further described herein. Such materials and associated selection and implementation are described herein in connection with idler 30, however, it should be appreciated that these teachings similarly apply to other embodiments described herein except where otherwise indicated.

As mentioned above, each of rim components 56 a and 56 b may include a stepped profile, as shown in FIG. 3. The stepped profile shown is relatively abruptly stepped, but need not be. In other embodiments, a more gradually stepped profile might be used. Rim components whose outer surface defines a uniform radius of curvature in an axial direction, however, would not likely be fairly considered to have a “stepped” profile as that term is intended to be understood herein. Each of rim components 56 a and 56 b may further include an outboard shoulder segment 60 a and 60 b, respectively, and an inboard crown segment 62 a and 62 b, respectively. Inboard crown segments 62 a and 62 b may abut another in a plane P. In one embodiment, rim components 56 a and 56 b may be mirror images of one another, and plane P may include a plane bisecting axis of rotation Z. Each of outboard shoulder segments 60 a and 60 b may be relatively tightly fitted upon outer peripheral surface 34 of hub 32 and may be located axially outward of radially projecting outer spine 48. Each of inboard crown segments 62 a and 62 b may be relatively loosely fitted, i.e. slip fitted, upon outer peripheral surface 34 and may axially overlap radially projecting outer spine 48. In one embodiment, each of outboard shoulder segments 60 a and 60 b may be interference fitted upon outer peripheral surface 34. To this end, idler 30 may include a first interference coupling 70 a between rim component 56 a and hub 32, and a second interference coupling 70 b between rim component 56 b and hub 32. Each of rim components 56 a and 56 b may also be relatively tightly fitted in abutment against outer spine 48, and relatively loosely fitted in abutment against each other. Another way to understand this principle is that outer spine 48 may be held in compression, or “sandwiched” axially between rim components 56 a and 56 b.

An axial thickness dimension AT₁ is defined by compound annular rim 50 and may be between about 200 millimeters and about 250 millimeters in one embodiment. Axial thickness AT₁ may more particularly be between about 215 millimeters and about 225 millimeters, and still more particularly equal to about 220 millimeters. It may be noted that outboard shoulder segments 60 a and 60 b may each comprise a relatively greater proportion of axial thickness AT₁ than do inboard crown segments 62 a and 62 b. Stated another way, outboard shoulder segments 60 a and 60 b may each include a first axial length/thickness, and inboard crown segments 62 a and 62 b may each include a second axial length/thickness greater than the first axial length/thickness. The axial length/thickness of each of inboard crown segments 62 a and 62 b may be equal to about 47.5 millimeters in one embodiment, with the remainder of axial thickness AT₁ comprised by outboard shoulder segments 60 a and 60 b together, and varying based upon an axial thickness of outer spine 48. Compound annular rim 50 may further include an inner rim surface 52 abutting outer peripheral surface 34 of hub 32. A radial thickness of rim components 56 a and 56 b, within outboard shoulder segments 60 a and 60 b, may be between about 20 mm and about 100 mm. Inner rim surface 52 may include a total of three concentric cylindrical surface segments, including a first cylindrical surface segment 68 a located on outboard shoulder segment 60 a, a second cylindrical surface segment 68 b located on outboard shoulder segment 60 b, and a middle cylindrical surface segment 68 c located in part upon inboard crown segment 62 a and also in part upon inboard crown segment 62 b.

Inner rim surface 52, and more particularly surface segments 68 a and 68 b may define an inner diameter dimension ID which may be equal to between about 625 mm and about 675 mm, more particularly equal to about 650 mm, and still more particularly equal to about 650.00 mm plus or minus tolerances of 0.00 mm and 0.05 mm, respectively. Outer peripheral surface 34 may define an outer diameter dimension also indicated generally via ID, equal to between about 625 mm and about 675 mm, more particularly equal to about 650 mm, and still more particularly equal to about 650.13 mm plus or minus tolerances of 0.05 mm and 0.00 mm, respectively. Track contacting outer rim surface 54, and more particularly portions of surface 54 upon inboard crown segments 62 a and 62 b, may define an outer diameter dimension OD₁ which may be equal to between about 645 mm and about 775 mm. As used herein, the term “about” may be understood in the context of a number of significant digits. Accordingly, about 650 mm means between 645 mm and 654 mm, and so on, except where otherwise indicated. Compound annular rim 50 may also be welded to hub 32. In one embodiment, a first annular weld 64 a which may include a circular edge weld attaches outboard shoulder segment 60 a to hub 32, and a second annular weld 64 b which may also include a circular edge weld attaches outboard shoulder segment 56 b to hub 32. In one embodiment, idler 30 may include a total of two welds, comprised by the two welds 64 a and 64 b attaching compound annular rim 50 to hub 32. Idler 30 may further consist essentially of rim components 56 a and 56 b, hub 32, and material of welds 64 a and 64 b.

Turning now to FIG. 4, there is shown an idler 130 for an undercarriage system in a track-type machine according to another embodiment. Idler 130 might be used in undercarriage system 14, or in any of the other undercarriage system and machine types contemplated herein. Idler 130 may include a one-piece hub 132 having an outer peripheral surface 134, an inner peripheral surface 144 defining an idler mounting bore 133, and a compound rim assembly 150 mounted upon hub 132. Compound rim assembly 150 and hub 132 may be understood as two components of an idler body 131. Compound rim assembly 150 may include a first annular track contacting rim 156 a, a second annular track contacting rim 156 b, and a track guiding ring 180. One or more welds may attach compound rim assembly 150 to hub 132, as further described herein. Idler 130 may have certain material properties similar to those properties described in connection with the foregoing embodiment, but having certain differences. Hub 132 may be formed of a relatively lower hardness metallic material, and certain parts of compound rim assembly 150 may be formed of a relatively higher hardness metallic material, but other components formed of non-metallic materials. Hub 132 may be formed of a relatively lower hardness metallic material, annular track contacting rims 156 a and 156 b may be formed of a relatively higher hardness metallic material, and track guiding ring 162 may be formed of a non-metallic material. In one embodiment, track guiding ring 180 may include a rubber material, having embedded reinforcements 182 such as metallic fiber reinforcements or the like. The use of a non-metallic material such as rubber may reduce noise resulting from ring 162 contacting track components such as track pins.

Compound rim assembly 150 may further include a one-piece annular base 160 configured for mounting rim assembly 150 upon outer peripheral surface 134. One-piece annular base 160 may be formed of a relatively lower hardness metallic material, having a hardness similar to hub 132, but not necessarily so, and includes a cylindrical inner surface 161 defining a center axis C. Center axis C may be overlapping with an axis of rotation Q of idler 130 defined by inner peripheral surface 144. Base 160 may further include a cylindrical outer surface 162 concentric with cylindrical inner surface 161, a first axial end surface 163, and a second axial end surface 167. Base 160 may also include an axial thickness AT₂ extending from first axial end surface 163 to second axial end surface 167, and a radial thickness RT₁ extending from inner cylindrical surface 161 to outer cylindrical surface 162 which is less than axial thickness AT₂. Base 160 may also include an interference coupling 135 with hub 132.

First annular track contacting rim 156 a may be positioned upon outer cylindrical surface 162 at a location adjacent first axial end surface 163, and second annular track contacting rim 156 b may be positioned upon outer cylindrical surface 162 at a location adjacent second axial end surface 167. Axial thickness AT₂ may be configured similarly to axial thickness AT₁ of idler 30. Radial thickness RT₁ may vary based upon a radial thickness RT₂ of rims 156 a and 156 b. In one embodiment, RT₂ may be configured similarly to the radial thickness of rim components 56 a and 56 b, described above. It will thus be understood that RT₁ might vary between a relatively greater thickness for a larger diameter of hub 132, and a relatively lesser thickness for a smaller diameter of hub 132. Hub 132 might include an outer diameter OD₂ between about 600 mm and about 700 mm in certain embodiments. An outer diameter OD₃ defined by an outer peripheral surface 184 of ring 180 may be between about 700 mm and about 800 mm, and may be equal to about 740 mm in one embodiment. Each of first annular track contacting rim 156 a and second annular track contacting rim 156 b may be welded to annular base 160. Track guiding ring 180 may be trapped axially between first and second rims 156 a and 156 b such that it abuts outer cylindrical surface 162 of base 160. As noted above, track guiding ring 180 may be formed of a non-metallic material, and projects radially outward of first and second rims 156 a and 156 b.

Rim assembly 150 may further include a first interference coupling 170 a between base 160 and first rim 56 a, and a second interference coupling 170 b between base 160 and second rim 156 b. Track guiding ring 180 may include an inner peripheral surface 186 slip fitted upon outer cylindrical surface 162, not actually attached to base 160, and thus held in place upon base 160 by way of being trapped between rim 156 a and rim 156 b. Also shown in FIG. 4 is a track pin 21 in contact with track guiding ring 180. Over the course of a service life of idler 130, it is expected that track guiding ring 180 may wear such that track pin 21 and other associated components of the track system may actually migrate relative to rims 156 a and 156 b until rims 156 a and 156 b begin to contact pins 21, or in other embodiments ride upon links 20. The description herein of “track pins” should be understood to refer to any type of suitable known track pin, including cartridge pins, and also track pins upon which a fixed or rotating bushing is positioned.

As discussed above, base 160 may be interference fit upon hub 132, and each of rims 156 a and 156 b may be interference fit upon base 160 via interference couplings 170 a and 170 b, respectively. In addition, welding may be used to couple together components of compound rim assembly 150, and to attach compound rim assembly to hub 132. To this end, a first weld 164 a attaches rim 156 a to base 160, and a second weld 164 b attaches rim 156 b to base 160. Base 160 may further include a first bevel surface 172 a extending from outer cylindrical surface 162 to first axial end surface 163, and a second bevel surface 172 b extending from outer cylindrical surface 162 to second axial end surface 167. First weld 164 a may include an annular weld such as a circular edge weld and including a weld material shown generally via reference numeral 174 contacting first bevel surface 172 a and also contacting rim 156 a. Second weld 164 b may also include an annular weld such as a second circular edge weld including weld material 174 contacting second bevel surface 172 b and also contacting rim 156 b. A third bevel surface 172 c and a fourth bevel surface 172 d may be formed on hub 132 and extend from outer peripheral surface 134 to first and second axial sides 140 and 142, respectively. Third and fourth welds 164 c and 164 d, also potentially circular edge welds, attach base 160 to hub 12. All the welds described herein may be formed by deep penetration welding procedures.

Idler 130 might include a newly manufactured idler shipped for installation into an existing undercarriage system of a track-type machine, or assembled with a newly manufactured track-type machine at the factory. Idler 130 may also include a remanufactured idler, where hub 132 includes a reusable hub, which is equipped with a new compound rim assembly at periodic service intervals. In this vein, compound rim assembly 150 may include a stand alone aftermarket component which is provided for replacement of a previously used compound rim assembly. In certain instances, upon track rebuild of an existing track-type machine using an idler such as idler 130, welds 164 c and 164 d may be machined or burned out, and interference coupling 135 reversed in preparation for installation of a substitute, new compound rim assembly similar to compound rim assembly 150 but not having yet experienced a service life. An interference coupling may then be established between the substitute compound rim assembly and the existing reusable hub in preparation for another service life of idler 130. Where provided as an aftermarket replacement part, compound rim assembly 150 may consist essentially of annular base 160, first and second rims 156 a and 156 b, weld material 174, and track guiding ring 180. A compound rim assembly provided as an aftermarket replacement part will thus be understood to include a total of two welds, namely, welds 164 a and 164 b, in certain embodiments. When rim assembly 150 is installed for service upon hub 132, the completed idler might include a total of four welds, including in addition welds 164 c and 164 d.

Referring now to FIG. 5, there is shown a rotatable idler 230 for an undercarriage system in a track-type machine having applications similar to the embodiments described above. Idler 230 may include a newly manufactured idler, but might also include a remanufactured idler as further described herein. Idler 230 may include a hub 232 which is a multi-piece hub having a main hub body 235, a plurality of removable body segments 237 a and 237 b, and a plurality of bolts 239 coupling body segments 237 a and 237 b to main hub body 235. In one practical implementation strategy, the plurality of removable body segments may include a number of body segments between two and six, although the present disclosure is not thereby limited. In FIG. 5, body segments 237 a and 237 b will be understood to curve in and out of the page, and thus may be understood as radial segments which when coupled with main hub body 235 together define an annular configuration. Hub 232 may be formed of a relatively lower hardness metallic material. A compound rim assembly 250 may be coupled with hub 232, and in one embodiment may include a first annular rim 256 a which is welded via an annular weld such as a circular edge weld 264 to each of removable body segments 237 a, 237 b, and such other removable body segments as might be used. Hub 232 may further include an outer hub surface 234 upon which first annular rim 256 a and a second annular rim 256 b are interference fitted. Rims 256 a and 256 b may be formed of a relatively higher hardness metallic material. It may be noted that outer peripheral surface 234 may be located in part upon main hub body 235 and also in part upon removable body segments 237 a and 237 b. In the embodiment of FIG. 5, a non-metallic track guiding ring 280 is trapped between rims 256 a and 256 b.

In contrast to the embodiment of FIG. 4, track guiding ring 280 may include a segmented ring having a plurality of radial ring segments, two of which are shown and identified via reference numerals 268 a and 268 b. A number of radial ring segments in idler 230 may be between two and six, but the present disclosure is not thereby limited. A plurality of connector bars 290 a and 290 b are coupled with radial segments 268 a and 268 b, respectively. A number of connector bars 290 a, 290 b coupled with radial segments 268 a, 268 b, may include a number of connector bars per each radial segment equal to at least two. In one embodiment, connector bars 290 a, 290 b, may be irreversibly coupled to radial segments 268 a, 268 b, such as by way of being integrally molded with a rubber material from which ring 280 is formed, and reversibly coupled to hub 232. Connector bars 290 a and 290 b may be trapped between body segments 237 a and 237 b and main hub body 235 in one embodiment. It will thus be understood that loosening bolts 239 can allow removal of an assembly comprised of rim 256 a and the removable body segments welded thereto. This might be done to enable replacement of track guiding ring 280, and reinstallation of segments 237 a, 237 b and rim 256 a. Alternatively to merely replacing track guiding ring 280, a replacement rim might be swapped for rim 256 a, and another replacement rim swapped for rim 256 b.

INDUSTRIAL APPLICABILITY

Returning to the embodiment of FIGS. 2 and 3, it will be recalled that compound annular rim 50 caps hub 32. Over the course of a service life of idler 30, material of rim components 56 a and 56 b may wear away. Prior to or upon reducing outer diameter of OD₁, by a certain amount, such as approximately two inches, it may be desirable to repair and/or remanufacture idler 30. Remanufacturing idler 30 may include removing compound rim 50 such as by machining or burning out welds 64 a and 64 b. Interference couplings 70 a and 70 b may be reversed to enable removal of rim components 56 a and 56 b, and reinstallation of new rim components. During capping hub 32 with replacement rim components, outer spine 48 may be sandwiched between the replacement rim components, and welds 64 a and 64 b formed. Establishing interference couplings 70 a and 70 b may be understood as reversibly coupling hub 32 with rim components 56 a and 56 b, whereas welds 64 a and 64 b may be understood to irreversibly couple the respective components. The remanufactured idler may then be returned to service.

Related techniques may be used to remanufacture an existing idler which includes a conventional one-piece casting. Those skilled in the art will be familiar with idlers of the type where a one-piece idler body is used. Such known idlers often include a central annular crown which serves to contact, tension, and guide an associated track. Over time, the center crown can wear, as may other outer surfaces of the idler. Strategies similar to those described above employing hard facing or other resurfacing techniques were previously used to repair idlers removed from service. It has been discovered that such techniques, while being quite labor intensive, also tend to result in an idler which is more susceptible to wear and has a reduced service life than new idlers. One of the reasons for this relates to inherent limitations of certain resurfacing techniques. Resurfacing can often require the addition of numerous layers of resurfacing material one at a time. Since each layer is deposited in the form of molten metallic material, heating of underlying layers inherently occurs. This tends to limit the types of materials which can be used in the hard facing or other resurfacing process, and can change the physical characteristics of materials comprising the underlying layers. As a result, engineers have previously been given little choice in how to go about repairing idlers of certain types.

The present disclosure allows idler repair to be driven not so much by the limitations of a particular process, but instead by the intended service applications of the subject idler to be repaired. Those skilled in the art will be familiar with different material compositions which are best suited to different operating environments for undercarriage system components in track-type machines. For example, certain materials may well suited to sandy operating environments, whereas other materials may be suitable for rocky operating environments. Similarly, different load bearing requirements, speed of rotation, temperature ranges experienced, and still other factors may be best addressed by different materials. Despite knowledge of different behavior of different materials, engineers have continued to produce remanufactured idlers having properties different to and often inferior from what would ideally be available. Thus, in the case of idler 30 and the other embodiments herein, rather than being forced to settle upon inferior materials due to process limitations, rim components 56 a and 56 b may be formed from materials best suited to a particular service application. Where an idler such as idler 30 is to be remanufactured multiple times, and its service environment changed, rim components 56 a and 56 b may be substituted for rim components which were used in the earlier service life but formed of a different material.

As alluded to above, idler 30 might include an idler originally manufactured as a one-piece casting, but remanufactured as a multi-component idler as shown. In preparation for remanufacturing an idler comprised of a single piece casting, it may be desirable to remove material from an outer periphery of the idler body to appropriate dimension the idler body for installation of rim components 56 a and 56 b, and also to provide clean and trued surfaces for establishing interference couplings 70 a and 70 b, and forming welds 64 a and 64 b. To this end, the outer surface of the existing idler may be reduced in diameter by removing material, but may be machined such that material remains to form/preserve outer spine 48.

Remanufacturing of idlers according to the embodiments of FIGS. 4 and 5 may take place in a manner somewhat different from the embodiment of FIGS. 2 and 3. In the case of the embodiment of FIG. 4, as noted above the entire compound rim assembly 150 may be removed from hub 132, and a new compound rim assembly positioned thereon and appropriately attached. In the FIG. 5 embodiment, as discussed above track guiding ring 280 might be replaced and/or rims 256 a and 256 b might be replaced.

The present description is for illustrative purposes only, and should not be construed to narrow the breadth of the present disclosure in any way. Thus, those skilled in the art will appreciate that various modifications might be made to the presently disclosed embodiments without departing from the full and fair scope and spirit of the present disclosure. Other aspects, features and advantages will be apparent upon an examination of the attached drawings and appended claims. 

What is claimed is:
 1. A rotatable idler for an undercarriage system in a track-type machine comprising: a one-piece hub defining an axis of rotation and being formed of a relatively lower hardness metallic material, the one-piece hub having an outer peripheral surface, a first and a second end surface located on first and second axial sides of the one-piece hub, an inner peripheral surface defining an idler mounting bore, and a radially projecting outer spine, the radially projecting outer spine having an annular configuration circumferential of the axis of rotation, and being positioned axially between the first and second end surfaces; and a compound annular rim coaxial with the one-piece hub and being formed of a relatively higher hardness metallic material, the compound annular rim capping the one-piece hub and including an inner rim surface, and a track contacting outer rim surface having a crowned profile; the compound annular rim further including a first and a second rim component, each of the rim components having a stepped profile, an outboard shoulder segment relatively tightly fitted upon the outer peripheral surface and located axially outward of the radially projecting outer spine, and an inboard crown segment relatively loosely fitted upon the outer peripheral surface and axially overlapping the radially projecting outer spine.
 2. The rotatable idler of claim 1 wherein each of the outboard shoulder segments is interference fitted upon the outer peripheral surface, and each of the inboard crown segments is slip fitted upon the outer peripheral surface.
 3. The rotatable idler of claim 2 wherein the inboard crown segments abut one another, and the outboard shoulder segments abut the radially projecting outer spine.
 4. The rotatable idler of claim 2 further comprising a first annular weld attaching the outboard shoulder segment of the first rim component to the one-piece hub, and a second annular weld attaching the outboard shoulder segment of the second rim component to the one-piece hub.
 5. The rotatable idler of claim 4 comprising a total of two welds attaching the compound annular rim to the one-piece hub.
 6. The rotatable idler of claim 4 wherein each of the first and second axial sides of the one-piece hub includes an axial side surface having a bathtub shaped profile of rotation about the axis of rotation of the idler.
 7. The rotatable idler of claim 6 wherein the first and second rim components are mirror images of one another, and the inboard crown segments abut one another at a plane bisecting the axis of rotation of the idler, and wherein the outboard shoulder segments include a first axial length, and the inboard crown segments include a second axial length greater than the first axial length.
 8. The rotatable idler of claim 7 wherein the inner surface of the compound annular rim includes a total of three concentric cylindrical surface segments.
 9. The rotatable idler of claim 8 wherein the concentric cylindrical surface segments include a first cylindrical surface segment located on the shoulder segment of the first rim component, a second cylindrical surface segment located on the shoulder segment of the second rim component, and a middle cylindrical surface segment located in part on the first rim component and also in part on the second rim component.
 10. A method of making a rotatable idler for an undercarriage system in a track-type machine comprising the steps of: capping a one-piece hub formed of a relatively lower hardness metallic material and defining an axis of rotation with a compound annular rim formed of a relatively higher hardness metallic material; sandwiching a radially projecting outer spine of the one-piece hub axially between abutting rim components of the compound annular rim during capping the one-piece hub; and attaching the compound annular rim to the one-piece hub; wherein the step of capping includes reversibly coupling the compound annular rim with the one-piece hub, and the step of attaching includes irreversibly coupling the compound annular rim with the one-piece hub.
 11. The method of claim 10 wherein the step of capping further includes a step of interference fitting a total of two rim components upon the one-piece hub, and wherein the step of attaching further includes welding the rim components to the one-piece hub with a total of two welds.
 12. The method of claim 11 wherein the step of sandwiching further includes relatively tightly abutting the rim components against the radially projecting outer spine, and relatively loosely abutting the rim components against one another.
 13. The method of claim 12 wherein the compound annular rim includes an outer rim surface having a crowned profile, wherein the step of interference fitting further includes interference fitting outboard shoulder segments of the rim components upon the one-piece hub, and the method further including a step of slip fitting inboard crown segments of the rim components over the radially projecting outer spine during capping the one-piece hub.
 14. The method of claim 13 wherein making the rotatable idler includes remanufacturing a rotatable idler removed from service in an undercarriage system for a track-type machine, and wherein the method further includes a step of removing material of the one-piece hub to reduce its diameter, prior to the step of capping the one-piece hub.
 15. An undercarriage system for a track-type machine comprising: a ground engaging track including a plurality of track shoes, and a plurality of track links coupling together the track shoes in an endless track chain; an idler for the ground engaging track including an idler body having a hub formed of a relatively lower hardness metallic material, and a compound annular rim capping the hub and being formed of a relatively higher hardness metallic material; the hub including an inner peripheral surface defining an idler mounting bore, an outer peripheral surface, and a radially projecting outer spine, and the radially projecting outer spine having an annular configuration and being concentric with the idler mounting bore; the compound annular rim having an inner rim surface, a track contacting outer rim surface having a crowned profile, and first and second abutting rim components sandwiching the radially projecting outer spine, each of the first and second abutting rim components having a stepped profile and including a portion of the inner rim surface and a portion of the track contacting outer rim surface; and a first interference coupling between the first rim component and the hub, and a second interference coupling between the second rim component and the hub.
 16. The undercarriage system of claim 15 further comprising a first annular weld attaching the first rim component to the hub, and a second annular weld attaching the second rim component to the hub.
 17. The undercarriage system of claim 16 wherein each of the first and second rim components includes an outboard shoulder segment, and an inboard crown segment, and wherein the first and second rim components are mirror images of one another and the inboard crown segments abut one another.
 18. The undercarriage system of claim 17 wherein the hub defines an axis of rotation and includes a first axial side, and a second axial side, and wherein each of the axial sides includes an axial side surface having a bathtub shaped profile of rotation about the axis of rotation. 